In the photoelectric sensor and the photoelectric sensor system that detect whether there is an object based on the difference between the levels of the received light signals when there is the object between the light emitting element and the light receiving element, in general, a pair of the light emitting element and the light receiving element is arranged such that an optical path from the light emitting element to the light receiving element is parallel to the axis of the object. However, when the object is thin, for example, when the object is a thin plate, the optical path parallel to the axis of the object is not shielded by the object, it is difficult to detect the object. Patent Document 1 discloses a method of detecting an object using a light emitting unit that emits a light signal and a light receiving unit that is provided in a different stage in a multi-optical axis photoelectric sensor in which a plurality of light emitting units and a plurality of light receiving units are arranged so as to be opposite to each other.
According to this method, the optical path from the light emitting unit to the light receiving unit has an angle with respect to the horizontal direction, that is, the optical path is inclined. Therefore, even though an object, which is a thin plate, is arranged such that the axis thereof is aligned with the horizontal direction, the optical path is shielded by the object. As a result, it is possible to detect the object.
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 8-148981